The Snowball Earth Hypothesis

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Contents
Introduction 3
Synoptic Description of the Snowball Earth Hypothesis 3
Causes of the Snowball Earth 5
Occurrence of the Snowball Effect 6
Impacts of the Snowball Effect 8
Personal Suggestions 9
Conclusion 10
Works Cited 12

Introduction

Massive changes in the earth’s climate are of particular note to environmental studies as they bear the potential to affect life greatly. Such geological and climatological changes are associated with the different ages that the earth has lived through, as well as the extinction and generation of various life forms. The Snowball Earth Hypothesis represents a concept explaining a possible climate and geological change in a past age in which the earth was entirely covered with ice. It explains contemporary observations about rock type distribution such as equatorial sedimentary deposits considered being from glacial origin (Cowen 50-51). This study analyzes the Hypothesis, providing a synoptic distribution, cause explanation, occurrence, and impact, before presenting a personal suggestion based on reflection on the evidence analyzed.

Synoptic Description of the Snowball Earth Hypothesis

The Snowball Earth Hypothesis focusses on the unparalleled climatic fluctuations that occurred during the Neoproterozoic time, positing that a global ice cover characterized this period. The hypothesis posits that the earth completely frozen, assuming a global ice cover, during the end of the Proterozoic era (Stern, Avigad, Miller, and Beyth 3). According to the proponents of the Snowball Earth, the earth was ice-covered from the poles to the equator during an extreme cooling event estimated at 580 million years ago. The Snowball Earth concept was put forward to explain observations that late Neoproterozoic ice sheets extended to sea level near the equator, as shown in figure 1.
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Figure 1: The global distribution of Neoproterozoic deposits from glaciation, indicating that very reliable amounts of glaciogenic deposits do occur within the tropics. This led to questions regarding how such a phenomenon occurred (Source: Hoffman and Schrag 130). This realization raised questions about the earth’s climate at the time, with climatologists and geologists pondering whether the tropics were colder than the poles, or whether an ice-albedo feedback caused such glacial presence at the equator (Hoffman and Schrag 129). Paleomagnetic and geological research into the several glacial deposits indicated that such deposits were formed at tropical latitudes. The Snowball Earth concept postulates that the low latitude glaciation observed resulted from an ice-albedo feedback runaway. The concept could also explain other geological observations such as the formation of banded iron deposits that occurred during the same period. Based on these explanations, a Snowball Earth represents the coldest climate possible on the planet, translating to a global mean temperature of -50°C following a reflection of the sun’s radiation by the ice cover (albedo concept). In such a scenario, equatorial temperatures would be -20°C, similar to that of present-day Antarctica. Further, the absence of a moderating ocean would translate to great day-night and seasonal temperature fluctuations. Glacial flow in a Snowball Earth would result in sedimentary deposits that indicate glacial activity even after transition from the Snowball Earth state (Snowball Earth Organization).

Causes of the Snowball Earth

Conceptual explanations suggest that the cause of a Snowball Earth entails the decline of atmospheric greenhouse gases including carbon dioxide and methane. This greenhouse gas reduction would itself arise from tectonically-mediated weathering of rocks caused by a dimmer sun than at present. The tropical distribution of continents is also a crucial aspect of the generation of a Snowball Earth, given their higher reflective power compared to oceans. In such a scenario, tropical continents absorb less solar energy than the oceans, an observation underpinned by contemporary observations that tropical oceans absorb most of the sun’s heat. The actual reduction of greenhouse follows weathering of silicate rocks to expose minerals that ionize carbon dioxide into bicarbonates. The bicarbonates react with oceanic Calcium ions, leading to deposition of calcium carbonate. This represents a transfer of atmospheric carbon dioxide, a greenhouse gas, to earth rock. Other contributors to the decline of greenhouses gases include the introduction of free atmospheric oxygen, reacting with methane to reduce the latter’s levels in the atmosphere. Further, a younger and weaker sun may have emitted about 6% less of radiation than it does today. The combination of reduced greenhouse gases and less radiation led to a cooler earth (Walker 238; Stern, Avigad, Miller, and Beyth 1-4). The tropical distribution of the planets led to increased reflection, which would have been replaced with solar absorption in case of tropical oceans. The lack of moderation to the cooling and continued weathering caused the polar ice to advance towards the tropics. Upon reaching 30° of the equator, a positive feedback unfolded in which the increased albedo (reflection sun’s radiation by the ice cover) effect causing further cooling and more glacial advance. This pattern continued rapidly until the entire earth was covered with ice (Huddart and Stott 830).

Occurrence of the Snowball Effect

Various geological sources of evidence confirm the Snowball Earth Hypothesis and represent modern occurrences of the fingerprints left by the phenomenon. One of the important ways to test the Snowball Effect Hypothesis is to evaluate whether the glacial units around the globe are synchronous, which should be the case if at all the effect occurred (Stern, Avigad, Miller, and Beyth 3). In this case, schematic variability of cap-carbonate sequences from various settings around the globe reveal similar patterns, suggesting a shared glaciogenic origin as indicated in figure 2. Further, Marinoan glacial rocks are distributed in Namibia and Enorama Creek in Australia.
[pic] [pic] Figure 2: A cap-carbonate sequence indicating the presence of glacial diamictite in Australia and Canada, as well as the Namibia, a tropical setting indicating equatorial distribution of the Snowball Earth fingerprints (Source: Hoffman and Schrag 132). Isotopic carbon analysis is also a major way of tracing the fingerprints of the Snowball Earth effect, leading to the identification of several tropical regions with glaciogenic rocks. Based on this method, other regions featuring heavy presence of Neoproterozoic rocks suggesting the Snowball Earth Effect include the Arabian-Nubian Shield and the East African Oregon (Figure 3). According to Stern, Avigad, Miller, and Beyth (5-7), the formation of the Arabian-Nubian Shield and the East African Oregon from the tectonic cycles of the East and West Gondwana reveals evidence of the Snowball Earth phenomenon based on the concept of tropical continents. The presence of Neoproterozoic dropstones around the world also indicates the occurrence of a Snowball Earth. For example, the Huqf Group dropstones in North Eastern Oman, within the tropics, contain proximal and distal glacial deposits, alongside other evidence of debris from marine deposits. Diamictite rocks originate from ancient glaciation, with their equatorial presence also serving as an evidence for the Snowball Earth occurrence. Such diamictite rocks are found in the Abu Maarah Group in North Oman (Stern, Avigad, Miller, and Beyth 7-8).
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Figure 3: The Arabian-Nubian Shield, another occurrence of Snowball Earth fingerprints (Source: Stern, Avigad, Miller, and Beyth 6).

Impacts of the Snowball Effect

A Snowball Earth occurrence would have far-reaching consequences on life on earth. One of the primary effects would be on seawater, which Hoffman and Schrag (146) indicate would experience changes in its elemental and isotopic composition. Sustained weathering and hydrothermal dominance would change the trajectories of carbonates and silicates in the seawater. The changes in carbonate and silicate levels would cause shifts in calcium concentration. Such seawater composition changes would lead to serious ramifications for sea life. The two scholars further explore the effect that a Snowball Earth phenomenon would have on Eukaryotes, noting the adaptive prokaryotic organisms would most probably survive the occurrence. The pertinent effects of the Snowball Earth to Eukaryotic organisms entail the thermal activity, nutrient level changes in seawater, and limited organic productivity. Further, glaciation would interfere with iron formation, limiting the availability of a major phosphorous sink. This indicates that the less-developed eukaryotes at the time of the Snowball effect may have faced extinction, with the phenomenon acting as an environmental filter on the evolution of life (147). A Snowball Earth occurrence today would obliterate most terrestrial eukaryotes owing to the drastic temperature change and reduced productivity. In the process, human civilization would be destroyed owing to the environmental changes accompanying a Snowball Earth occurrence. Further, surviving organisms would face difficult conditions during the Snowball deglaciation period (Abbot, Raymond, and Pierrehumbert 1). According to Hoffman et al. (1), the oceanic freeze characterizing a Snowball Earth would shut down the hydrologic cycle and, as a result, prevent primary productivity. In the absence of primary productivity, all other dependent life forms would be affected. Based on thermodiffusion, the average surface temperatures would fall drastically while the ice cover increases in thickness. The thickened ice cover would lead to the absence of a carbon sink through the prevention of weathering and photosynthesis. The carbon sink absence would cause an accumulation of atmospheric carbon dioxide, requiring millions of years to reverse the albedo effect. At a critical atmospheric level, reversal of the glaciation at the equator would occur, causing ocean clearance at the tropics. Absorption of carbon dioxide into the ocean would build up calcium ions and bicarbonate levels, leading to the reestablishment of biological life. In all projections, a Snowball Earth would serve as an environmental sieve on evolution. Ward (79) indicates that the Snowball Earth phenomenon 580 million years ago caused evolutionary realignment through its effects on prokaryotes and eukaryotes. The Snowball event led to an end to the lengthy periods of highly toxic oceans containing high levels of hydrogen sulphide and low oxygen. As a result, the first animal phyla emerged following the Snowball Earth occurrence.

Personal Suggestions

The effects of a Snowball Earth indicate serious consequences for existing organisms, meaning that a similar occurrence may signal the end of human civilization. Although the causes of a Snowball Earth involve major planetary climatic factors, an anthropogenic role may contribute to accelerating or sparking such factors. For example, human activities such as fossil fuel use lead to changes in the levels of greenhouses gases. Further, anthropogenic activities may interfere with carbon and other elemental sinks directly or indirectly. In such scenarios, the effects of humans interfere with some of the elements involved in a Snowball Earth. As a result, efforts to conserve the natural biogeochemical cycles such as carbon, hydrological, and phosphorus cycles should be undertaken to prevent geological and climatic consequences that may cause large-scale global environmental transformations such as the Snowball Earth. Such preventive strategies are crucial because, as Walker (238) notes, a Snowball may begin upon the influence of some trivial cooling trigger, which may be manmade. Peltier Liu and Crowley (813-818) indicate that dissolved organic carbon remineralization may prevent a Snowball. This would only happen in case the carbon cycle is not interrupted, indicating that human actions may indirectly allow the phenomenon to be triggered.

Conclusion

The Snowball Earth Hypothesis postulates that the earth was completely frozen, having an ice cover from the poles to the equator during the end of the Proterozoic era about 580 million years ago. The Snowball Earth was caused by a set of factors that altogether led to cooling and rapid glacial advancement to the tropics. These factors include a decline in the level of decline of atmospheric greenhouse gases, tropical distribution of continents, and a less luminous sun. The cooling allowed glacial ice to spread to within 30° of the equator, which led to an albedo effect of increased cooling and rapid ice cover increase. In terms of occurrence, Marinoan glacial rocks are distributed in Namibia and Enorama Creek in Australia, other neoproterozoic rocks in the Arabian-Nubian Shield and the East African Oregon, and neoproterozoic dropstones in North Eastern Oman. Some of these areas are within the tropics, confirming glaciogenic sedimentation. A Snowball effect would cause rapid environmental changes that would affect both prokaryotes and eukaryotes, in the process wiping out human civilization. Conserving the environment to protect geochemical cycles for elements such as carbon may prevent an anthropogenic trigger to a Snowball Earth.

Works Cited

Abbot, Dorian S., and Pierrehumbert, Raymond T. “Mudball: Surface Dust and Snowball Earth Deglaciation.” Journal of Geophysical Research, 115 (2010): 1-11. Print.
Cowen, Richard. History of Life. Malden: Blackwell Publishing, 2005. Print.
Hoffman, Paul F., Daniel P. Schrag. “The Snowball Earth Hypothesis: Testing the Limits of Global Change.” Terra Nova, 14.3 (2002): 129-155. Print.
Hoffman, Paul F, Daniel P. Schrag, Galen P. Havelson, Alan J. Koufman, Samuel A. Bouring, and Raymond T. Pierrehumbert. Neoproterozoic Snowball Earth. Yale University, 1999. Web. 7 April, 2013.
Huddart, David, and Tim Stott. Earth Environments: Past, Present and Future. Hoboken: John Wiley & Sons, 2010. Print.
Peltier, Rochard W., Yonggang Liu, and John W. Crowley. “Snowball Earth prevention by dissolved organic carbon remineralization.” Nature, 450 (2006): 813-818. Print.
Snowball Earth Organization. What is Snowball Earth? Web. 7 April, 2013.
Stern, R., D. Avigad, M. Miller, and N. Beyth. “Evidence for the Snowball Earth Hypothesis in the Arabian Nubian Shield and the East African Oregon.” Journal of African Earth Sciences, 44 (2006): 1-20. Print.
Walker, Gabrielle. Snowball Earth. New York: Bloomsbury Publishing, 2003. Print.
Ward, Peter. The Medea Hypothesis: Is Life on Earth Ultimately Self-Destructive? Princeton: Princeton University Press, 2009. Print.